Optical topography

Optical topography (OT) was proposed in 1995 as a new imaging method for observing brain activity. It can bring out meaningful information such as spatio-temporal blood volume and oxygenation changes in cortices, and its facility can allow non-invasive measurement of human brain function under various conditions without restriction on the subjects. Researchers are beginning to use OT to investigate brain functions, and for clinical applications. In this paper, we introduce the evolution of the OT system and present a few results of brain functional measurement and clinical uses. The development of OT was advanced on 4 steps. The first generation system had only one probe with dual wavelengths. Therefore in order to reconstruct topographic images of cortical activity the probe had to be manually moved for 10 measurement positions. The second system was able to measure 12 positions, which were sequentially sampled by using a multiplexer and an optical switching device, in 6 seconds. The third system was developed to evaluate simultaneous measurement of 8 positions. At present, we finished the fourth OT system having 24 measurement channels with dual wavelengths. Using this system, we are performing dynamical observations of hemodynamic changes during brain activation and epileptic seizures.